|
Choosing a
Grating/Central Wavelength
The grating you choose is the main optical element that determines
the spectral resolution of your observations. The following Table gives the
details of the various COS gratings, the corresponding wavelength coverage,
spectral resolution, etc.
COS Spectroscopic Modes
|
Grating
|
Useful
wavelength range (Å)
|
Bandpass
per exposure (Å)
|
Resolving
Power R =l/Dl
|
Dispersion
(mÅ pixel-1)
|
|
FUV Channel
|
|
G130M
|
1150 -1450
|
292
|
20,000-24,000
|
9.97
|
|
G160M
|
1405 -1775
|
360
|
20,000–24,000
|
12.23
|
|
G140L
|
1230 -2050
|
>820
|
2,000-5,000
|
80.3
|
|
NUV Channel
|
|
G185M
|
1700 -2100
|
3 × 35
|
16,000–20,000
|
37
|
|
G225M
|
2100 -2500
|
3 × 35
|
20,000–24,000
|
33
|
|
G285M
|
2500 -3200
|
3 × 41
|
20,000–24,000
|
40
|
|
G230L
|
1700 -3200
|
(1 or 2) × 398
|
1,550-2,900
|
390
|
You must choose an appropriate central wavelength so that the
wavelength of interest falls on an active area of the detector. See the
tables below for both the FUV and NUV nominal wavelength setting ranges. If
the wavelength of interest falls between the segment or stripe gaps or it
is not in the supported wavelength range for the chosen grating, the ETC
will generate an error page.
Wavelength Ranges for FUV Gratings
|
Grating
|
Nominal wavelength
setting (Å) 1
|
Recorded wavelengths
|
|
Segment B
|
Segment A
|
|
G130M
|
1291
|
1132-1274
|
1291-1433
|
|
1300
|
1141-1283
|
1300-1442
|
|
1309
|
1150-1202
|
1309-1451
|
|
1318
|
1159-1301
|
1318-1460
|
|
1327
|
1168-1310
|
1327-1469
|
|
G160M
|
1577
|
1382-1556
|
1577-1752
|
|
1589
|
1394-1568
|
1589-1764
|
|
1600
|
1405-1579
|
1600-1775
|
|
1611
|
1416-1590
|
1611-1786
|
|
1623
|
1428-1602
|
1623-1798
|
|
G140L
|
1105
|
<300-970
|
1105-2253
|
|
1230
|
<300-1095
|
1230-2378
|
1 The nominal wavelength setting has
been chosen to be the shortest wavelength that is adjacent to the gap on
segment A so that the indicated wavelength is an actually recorded one.
Wavelength Ranges for NUV Gratings
|
Grating
|
Nominal wavelength setting (Å)
|
Recorded wavelengths
|
|
Stripe A
|
Stripe B
|
Stripe C
|
|
G185M
|
1786
|
1670 - 1705
|
1769 - 1804
|
1868 - 1903
|
|
1817
|
1701 - 1736
|
1800 - 1835
|
1899 - 1934
|
|
1835
|
1719 - 1754
|
1818 - 1853
|
1916 - 1951
|
|
1850
|
1734 - 1769
|
1833 - 1868
|
1931 - 1966
|
|
1864
|
1748 - 1783
|
1847 - 1882
|
1945 - 1980
|
|
1882
|
1766 - 1801
|
1865 - 1900
|
1964 - 1999
|
|
1890
|
1774 - 1809
|
1872 - 1907
|
1971 - 2006
|
|
1900
|
1783 - 1818
|
1882 - 1917
|
1981 - 2016
|
|
1913
|
1796 - 1831
|
1895 - 1930
|
1993 - 2028
|
|
1921
|
1804 - 1839
|
1903 - 1938
|
2002 - 2037
|
|
1941
|
1825 - 1860
|
1924 - 1959
|
2023 - 2058
|
|
1953
|
1837 - 1872
|
1936 - 1971
|
2034 - 2069
|
|
1971
|
1854 - 1889
|
1953 - 1988
|
2052 - 2087
|
|
1986
|
1870 - 1905
|
1969 - 2004
|
2068 - 2103
|
|
2010
|
1894 - 1929
|
1993 - 2028
|
2092 - 2127
|
|
G225M
|
2186
|
2070 - 2105
|
2169 - 2204
|
2268 - 2303
|
|
2217
|
2101 - 2136
|
2200 - 2235
|
2299 - 2334
|
|
2233
|
2117 - 2152
|
2215 - 2250
|
2314 - 2349
|
|
2250
|
2134 - 2169
|
2233 - 2268
|
2332 - 2367
|
|
2268
|
2152 - 2187
|
2251 - 2286
|
2350 - 2385
|
|
2283
|
2167 - 2202
|
2266 - 2301
|
2364 - 2399
|
|
2306
|
2190 - 2225
|
2288 - 2323
|
2387 - 2422
|
|
2325
|
2208 - 2243
|
2307 - 2342
|
2406 - 2441
|
|
2339
|
2223 - 2258
|
2322 - 2357
|
2421 - 2456
|
|
2357
|
2241 - 2276
|
2340 - 2375
|
2439 - 2474
|
|
2373
|
2256 - 2291
|
2355 - 2390
|
2454 - 2489
|
|
2390
|
2274 - 2309
|
2373 - 2408
|
2472 - 2507
|
|
2410
|
2294 - 2329
|
2393 - 2428
|
2492 - 2527
|
|
G285M
|
2617
|
2480 - 2521
|
2596 - 2637
|
2711 - 2752
|
|
2637
|
2500 - 2541
|
2616 - 2657
|
2731 - 2772
|
|
2657
|
2520 - 2561
|
2636 - 2677
|
2751 - 2792
|
|
2676
|
2539 - 2580
|
2655 - 2696
|
2770 - 2811
|
|
2695
|
2558 - 2599
|
2674 - 2715
|
2789 - 2830
|
|
2709
|
2572 - 2613
|
2688 - 2729
|
2803 - 2844
|
|
2719
|
2582 - 2623
|
2698 - 2739
|
2813 - 2854
|
|
2739
|
2602 - 2643
|
2718 - 2763
|
2837 - 2878
|
|
2850
|
2714 - 2755
|
2829 - 2870
|
2945 - 2986
|
|
2952
|
2815 - 2856
|
2931 - 2972
|
3046 - 3087
|
|
2979
|
2842 - 2883
|
2958 - 2999
|
3073 - 3114
|
|
2996
|
2859 - 2900
|
2975 - 3016
|
3090 - 3131
|
|
3018
|
2881 - 2922
|
2997 - 3038
|
3112 - 3153
|
|
3035
|
2898 - 2939
|
3014 - 3055
|
3129 - 3170
|
|
3057
|
2920 - 2961
|
3036 - 3077
|
3151 - 3192
|
|
3074
|
2937 - 2978
|
3053 - 3094
|
3168 - 3209
|
|
3094
|
2957 - 2998
|
3073 - 3114
|
3188 - 3229
|
|
G230L
|
2635
|
1371 - 17581
|
2450 - 2848
|
1795 - 19922
|
|
2950
|
1672 - 2071
|
2761 - 3160
|
1950 - 21472
|
|
3000
|
1731 - 2130
|
2821 - 3219
|
1979 - 21772
|
|
3360
|
2098 - 2497
|
3190 - 3586
|
2162 - 23602
|
|
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